Manufacturing Bits: May 2

Patterning 1nm features
The Center for Functional Nanomaterials (CFN) at the Brookhaven National Laboratory has patterned features down to 1nm using a direct-write lithography technique.

Using a scanning transmission electron microscope (STEM), researchers have patterned thin films of the polymer poly(methyl methacrylate), or PMMA, down to 1nm with a spacing between features at 11nm.

Researchers described the process as electron-beam lithography (EBL). Technically, though, an e-beam lithography tool and STEM are different. A traditional e-beam tool is used for direct-write lithography applications, while a STEM is typically used as a metrology tool.

Regardless, to accomplish this feat, researchers installed a pattern generator in the STEM. A pattern generator moves the electron beam over a sample to pattern features. The system is “a special scanning TEM with a spot size at the atomic scale,” said Vitor Manfrinato, a research associate in CFN’s electron microscopy group, in an e-mail.

With the system, researchers devised structures smaller than 5nm. This was for both gold palladium and zinc oxide materials. The gold palladium features were as small as six atoms wide, according to researchers.

A schematic showing a focused electron beam (green) shining through a polymeric film (Source: Brookhaven National Laboratory)

Using this technique, polymer films can be patterned at sizes much smaller than the 26nm effective radius of a PMMA macromolecule, according to researchers. “The polymer chains that make up a PMMA macromolecule are a million repeating monomers (molecules) long—in a film, these macromolecules are all entangled and balled up,” said Aaron Stein, a senior scientist in the electronic nanomaterials group at CFN, on the group’s Web site. “We were surprised to find that the smallest size we could pattern is well below the size of the macromolecule and nears the size of one of the monomer repeating units, as small as a single nanometer.”

Manfrinato added: “Our goal at CFN is to study how the optical, electrical, thermal, and other properties of materials change as their feature sizes get smaller. Until now, patterning materials at a single nanometer has not been possible in a controllable and efficient way.”

Measuring snowflakes
Using a special multi-angle camera, École Polytechnique Fédérale de Lausanne (EPFL) has gained some insights into the structures of snowflakes.

Researchers installed cameras in two locations. The first was a site near Davos, a town in the Swiss Alps. The second was Adélie Land, a site in coastal Antarctica.

At those locations, EPFL took pictures of thousands of snowflakes from three different angles at an altitude of 2,500 meters. Researchers used what they call a multi-angle snowflake camera. It makes use of three synchronized cameras, which take high-resolution images of snowflakes when they go through a metallic ring.

EPFL’s Multi-Angle Snowflake Camera (Source: LTE/EPFL)

Researchers took 3,500 of these images. Then, they developed a machine learning algorithm. The algorithm classifies the snowflake images into six main classes–planar crystals, columnar crystals, graupels, aggregates, combination of column and planar crystals, and small particles, according to EPFL.

The six families of snowflakes (Source: LTE/EPFL)

“Most of the snowflakes in the Alps are aggregates (49%), followed by small particles and graupels. However, in Antarctica, the majority were small particles (54%), followed by aggregates and graupels,” according to EPFL.

“The scientific community has been trying to improve precipitation measurement and forecast for over 50 years. We now have a pretty good understanding of the mechanisms involved in rain,” said Alexis Berne on EPFL’s site. “But snow is a lot more complicated. Many factors–like the shape, geometry and electromagnetic properties of individual snowflakes–affect how snow crystals reflect signals back to weather radars, making our task much harder. And we still don’t have a good grasp of the equivalent liquid water content of snowflakes. Our goal with this study was to better understand exactly what’s falling when it snows, so that we can eventually improve snowfall forecast at high altitudes.”

Beam splitters
Spectroscopy is a metrology technique to analyze materials. The technology splits a single beam of light into two in order to measure changes in a sample. In a system, a beam-splitter is used to separate a single beam into two separate beams. But generally, beam splitters have been limited to light beams using partially reflective glass, according to EPFL.

The new method solves some problems. 3D printing presents no limitations on possible shapes. And the plating process enables robust elements. Researchers from EPFL started the process by developing a plastic piece using a 3D printer. The plastic piece was selectively pre-treated with a conductive layer. Some areas of the device were metallic and conductive. Still other areas were insulators.

Then, researchers electroplated a 10μm-thick metal layer on the structure, enabling them to build two electrically independent high-voltage electrodes. This, in turn, enables a beam splitter with an electrostatic hexapole guide, which transforms into two bent quadrupoles.